Abstract
Collectin liver 1 (CL-L1, alias collectin 10) and collectin kidney 1 (CL-K1, alias collectin 11) are oligomeric pattern recognition molecules associated with the complement system, and mutations in either of their genes may lead to deficiency and developmental defects. The two collectins are reportedly localized and synthesized in the liver, kidneys, and adrenals, and can be found in the circulation as heteromeric complexes (CL-LK), which upon binding to microbial high mannose-like glycoconjugates activates the complement system via the lectin activation pathway. The tissue distribution of homo- vs. heteromeric CL-L1 and -K1 complexes, the mechanism of heteromeric complex formation and in which tissues this occurs, is hitherto incompletely described. We have by immunohistochemistry using monoclonal antibodies addressed the precise cellular localization of the two collectins in the main human tissues. We find that the two collectins have widespread and almost identical tissue distribution with a high expression in epithelial cells in endo-/exocrine secretory tissues and mucosa. There is also accordance between localization of mRNA transcripts and detection of proteins, showing that local synthesis likely is responsible for peripheral localization and eventual formation of the CL-LK complexes. The functional implications of the high expression in endo-/exocrine secretory tissue and mucosa is unknown but might be associated with the activity of MASP-3, which has a similar pattern of expression and is known to potentiate the activity of the alternative complement activation pathway.
Highlights
The innate immune system is a first line of defense and plays major roles in preventing microorga nisms in settling and becoming pathogens, and in the mounting of suitable immune responses against eventual pathogens
Collectin liver 1 (CL-L1) and collectin kidney 1 (CL-K1) Tissue Localization is a “self-amplificative“ cascade system, mainly found in the blood, and includes several pattern recognition molecules (PRMs); among which some activate a pathway known as the lectin activation pathway, via activation of serine proteases known as Mannan-binding lectin (MBL)-associated serine protease (MASP-1, -2, and -3) [2, 3]
The reactivity of the applied MAbs was demonstrated by Western blotting using serum as source of antigens (Figure 1). This analysis showed that the applied MAbs 16-13 and 11-1 only reacted with protein bands correlating with the molecular weight of CL-L1 and CL-K1, respectively (Figure 1) [7]
Summary
The innate immune system is a first line of defense and plays major roles in preventing microorga nisms in settling and becoming pathogens, and in the mounting of suitable immune responses against eventual pathogens. It often relies on recognition and binding to pathogen-associated molecular patterns by host pattern recognition molecules (PRMs). Mannan-binding lectin (MBL) is probably the most studied PRM of the lectin activation pathway and binds to mannose-rich glycoconjugates on the surface of microorganisms, initiating complement activation. MBL deficiency may increase susceptibility toward infections in certain situations but not in general [4], most likely contributed by coincidental activation of different complement activation pathways by a given microorganism
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